Hi i was called into meeting by my son's teacher yesterday. they are concerned about his concentration. what do i do from here? please help

Have an assessment: You didn't list age or other symptoms but the process is the same for all. Having the kid evaluated by an educational psychologist to identify problems with learning style, focus, concentration, etc. are all features needed to succeed in the classroom. If s/he finds an attention or learning problem it can be addressed. Teachers are good at identifying kids who struggle, but not always why.